The present invention relates generally to speaker cones and cone assemblies, and more particularly to a speaker cone comprising a composite material and to a cone assembly comprising the cone bonded to a surround, and to methods of making the same.
Loudspeaker diaphragms are used to convert electric vibrations into mechanical vibration; the most common type is a cone assembly which generates acoustic sound by mechanical vibration of the cone. A cone assembly generally comprises a cone and a suspension member. The cone is a sound radiating cone which generally has a frustoconical configuration with a concave curvilinear profile. A cone is generally circular in shape, with a circular outer peripheral edge and a circular annular neck which may extend in the axial direction of the cone. This neck is at the center of the cone, and is referred to as a xe2x80x9cvoice coil inside diameter,xe2x80x9d or VCID; it is open, and may be attached to a voice coil or the like in a conventional manner. The cone is adapted to be supported on a support frame through an annular suspension member or rim, which is secured to the outer marginal edge of the cone and which has predetermined elastic or flexibility properties. Such a suspension member may also be referred to as a roll edge or as a surround. The surround may be formed as an integral generally radially directed extension of the outer marginal edge of the cone, or it may be formed as a separate annular supporting flange or rim which is then affixed to the outer marginal edge of the cone.
Various materials have been used in the construction of loudspeaker cones, including metal, woven fabric, films of plastic, and pulp comprised of natural fibers or synthetic fibers, such as carbon fibers, glass fibers, and kevlar or acrylic. Two commonly used materials are paper pulp and plastic. Paper cones are generally prepared by forming cellulose fibers of paper to a certain configuration using a mold. Such cones are also referred to as fibrous or felted paper-type cones. Plastic cones are generally prepared by one of two ways; one way is shaping pellets of plastic resin into a film, and then vacuum molding the film to form a cone, and the other way is by directly injection molding the resin form into a cone shape.
Many properties of a speaker cone depend upon the material from which the cone is constructed. Such properties include the acoustic properties, the durability of the cone, the change in the acoustic properties of the cone over time, and the ability of the cone to withstand environmental conditions such as high and low temperature, moisture and ultra violet light. The cost of manufacturing speaker cones also depends upon the cone material.
Paper cones offer several advantages over plastic cones. Typically a paper cone has a wider acoustic range, as it has more varied capabilities and greater flexibility during its manufacture in terms of controlling its stiffness. Thus, a paper cone may be made harder or softer, such as by pressing or by chemical treatments; this flexibility of manufacture does not exist with plastic, as the same treatments have no effect on plastic cones. The performance of a paper cone is also superior to that of a plastic cone, where performance is defined as how much sound level is obtained per watt of power driving the speaker; this is because paper cones are generally stiffer at lighter weights than plastic ones, and the lighter the speaker, the less power it takes to drive it. In addition, the frequency range of a paper cone is much greater for a single paper cone than for a plastic polymer cone of similar dimensions. Thus, in instances where a single paper cone in a speaker assembly might suffice, it would take two or more plastic cones to match the sound range of the single paper cone.
The advantages of plastic cones include increased versatility in appearance; such versatility exists in the greater differences in color, surface sheen, and shapes which can be obtained with plastic cones. Furthermore, the sound quality of plastic cones tends to be more uniform in different environments and over time, as the cellulose material of a paper cone is strongly influenced by humidity. However, the performance of plastic cones is typically more influenced by temperature than is the performance of paper cones.
The material of a speaker cone also influences the type of surround which can be used with it. The relatively high amplitude vibrations in the axial direction of the speaker cone, to which dynamic or moving coil-type loudspeaker cones used for mid low frequency ranges are subjected, dictates that the surround be both flexible and durable. In the past, surrounds were made from rubber; however, rubber surrounds are generally expensive. Less expensive surrounds have been made from cloth, from a thermoplastic elastomer or from polyurethane foam material. These surrounds have been pre-fabricated and then attached to the outer marginal edge of a cone with adhesives. However, such surrounds have several drawbacks. One is that the selection of starting materials is limited. Another is that fabrication of such surrounds generally involves stamping or cutting out the surround form from sheets of material, resulting in considerable waste of starting material. Yet another is that such surrounds must be attached to speaker cones, usually by means of an adhesive; however, the choice of effective adhesives is limited, and even with the better adhesives, the resulting bonds between the surrounds and the cone are often less than optimal. Furthermore, the glue adds weight to the cone. Additionally, there may be considerable variation in the alignment between the surround and the cone, which may affect acoustic properties of the cone. Finally, fabrication and attachment of such surrounds require skilled hand assembly, and thus additional time and expense of manufacture.
Alternatively, polymer based surrounds have been molded onto speaker cones. By over molding it is meant that the surround is formed and attached to a cone in a single molding process, in which the outer peripheral edge of the cone is exposed to the polymeric surround material during the molding procedure. Different types of surrounds have been used in different molding procedures with different types of cones.
In one type of molded surrounds, foam surrounds have been fabricated and attached to a felted paper-type cone by molding the surround to the cone, as disclosed in U.S. Pat. No. 5,319,718. Such surrounds are prepared by a low pressure casting process, where a liquid polyurethane foam is placed in an open mold in contact with the outer marginal edge of the cone; the mold is then closed, and the foam is expanded and cured. The result is a cone assembly with a foam surround which is molded onto the outer marginal edge of the cone, where the surround forms a mechanical bond with the cone as a result of impregnation of the surround material into the fibrous material of the cone.
In yet another type of molded surrounds, an elastomeric surround can be injection-molded onto an injection molded cone, as is disclosed in EPO 552040 B1. In this case, the surround is formed by injecting an elastomeric material into a closed mold which also contains the cone; the outer peripheral edge of the cone comes into contact with the elastomeric material. The result is a cone assembly with an elastomeric surround molded onto the outer marginal edge of the cone. As disclosed by EPO 552040 B1, the cone is also formed by injection molding, and preferably the material of the cone and of the surround are selected such that when the surround is injection molded onto the cone, the cone and the surround are chemically bonded to each other. By chemically bonded it is meant that the two become attached at a molecular level, due to cross-linking of the respective materials.
Attempts have been made to assemble paper cones with molded polymeric surrounds. However, several problems were encountered. One problem is poor attachment of an elastomeric surround with a paper cone. Attempts to injection mold an elastomeric surround onto a pure cellulose fiber material cone resulted in no bond formation, or very minimal bond formation, between the cone and the surround. By minimal bond formation it is meant that a molded elastomeric surround was easily detached or removed from the paper cone by the application of minimal force, which is quite unsatisfactory.
Another problem encountered is the formation of flash during the injection molding procedure. Flashing is defined as various points where the elastomer has seeped onto the surface of the paper cone during the injection molding procedure. Flashing is hypothesized to occur at least in part because paper is more compressible than plastic, and under the high pressure of the injection molding procedure, when the elastomer is forced into the mold cavity, the elastomer displaces the soft paper and pushes on inward, causing flashing to occur. Flashing results in an increase in cone weight, due to the presence of more material, and it is also cosmetically undesirable. Too much flash may affect performance of the cone.
Yet another problem encountered during attempts to injection mold an elastomeric surround to a paper cone is the formation of narrow witness marks during the injection molding procedure. Witness marks are the result of compressing the paper during the molding procedure; the paper is compressed when the molding tool closes upon it. Narrow witness marks are undesirable both structurally and cosmetically. Structurally, narrow witness marks are unacceptable because they result in a hinging effect, which means that the paper is depressed to the point that the cone is weakened. This weakened area affects the performance of the cone, either acoustically in affecting the sound, or in the ability of the cone to handle the power of the speaker. This weakened area is also prone to breakage. In addition, narrow witness marks are considered objectionable on a cosmetic basis, resulting in a less desirable appearance.
Thus, there is a need to provide a felted paper-type cone to which it is possible to attach a surround by molding, which results in with a strong bond between the cone and the surround. There is also a need to provide a process by which a surround may be over molded to a cone without the appearance of flashing or witness marks.
It is an object of the present invention to provide a material for manufacturing a felted paper-type loudspeaker cone to which it is possible to attach a surround by molding the surround onto the cone, where the surround bonds strongly to the cone without the appearance of flashing or the appearance of witness marks.
It is also an object of the present invention to provide a material for manufacturing a felted paper-type cone which is less susceptible to environmental conditions.
It is yet a further object of the present invention to provide a speaker cone assembly comprising a cone manufactured from the material of the invention and a surround molded onto the peripheral outer edge of the cone and strongly bonded to the material present in the cone during the molding procedure. The loudspeaker cone assembly may further include additional elements attached to the outer rim of the surround, where such additional elements are also attached to the surround during the molding procedure. Such additional elements include means for securing the surround to the speaker chassis.
These and other objects of the present invention are achieved by providing a speaker cone assembly comprising a felted paper-type cone and a molded surround which is formed and bonded to the cone during molding, where the cone material is a composite material comprising a mixture of natural fibers and synthetic fibers, and where at least some of the synthetic fibers are able to chemically bond with at least some components in the surround material.
In addition, a method for producing a composite material for use in manufacturing a felted paper-type cone is also provided, where the method comprises mixing natural fibers and synthetic fibers to form a pulp, such that at least some of the synthetic fibers are able to chemically bond with at least some components in the material of a molded surround.
Furthermore, a method for producing a speaker cone assembly comprising a felted paper-type cone and a molded surround is also provided, where the method includes molding a surround to a cone such that the surround is formed and bonded to the cone during the molding procedure, where the cone is manufactured from a composite material comprising a mixture of natural fibers and synthetic fibers, such that at least some of the synthetic fibers are able to chemically bond with at least some components in the material of the molded surround. The method may also include attaching additional elements to the outer rim of the surround during the molding procedure.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only. Indeed, various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.